The present invention relates to a pressure retaining device, a pressure retaining system, and an ink jet printer.
A conventional maintenance (pressure retaining) mechanism comprises, for example as shown in FIG. 1, a printing head 101 having a set of nozzles arranged in rows, an ink cartridge 102 for storing ink to be supplied to the printing head 101, an air pump 103 for pumping compressed air, and a charge tank 104 connected across an air passage between the ink cartridge 102 and the air pump 103 for temporarily storing the compressed air. The conventional maintenance mechanism further includes, for example, an open/close relief valve 105 connected across an air passage between the charge tank 104 and the air pump 103 and a compressing open/close valve 106 connected across an air passage between the ink cartridge 102 and the charge tank 104, thus allowing the compressed air generated by the air pump 103 to be applied to the ink in the ink cartridge 102 for positive pressure purging and then exposure to the atmosphere after a predetermined length of time.
When employed in an ink jet recording apparatus, the conventional maintenance mechanism may be accompanied with a carriage which carries a printing head and a sub tank unit. The conventional maintenance mechanism also includes an ink cartridge connected by a supply tube to the printing head, an air pump for supplying the ink cartridge with compressed air, a pressure regulator, and a switching valve. When the storage of ink in the sub tank becomes smaller, the switching valve is turned on for communicating between the air pump and an ink bag in the ink cartridge. This permits the compressed air to be delivered from the air pump via the pressure regulator and the switching valve to the ink bag from which the ink is transferred to the printing head or the sub tank (See Japanese Patent Application Laid-Open No. 10-138506, Paragraphs 0030 to 0037 and FIGS. 3 and 4).
However, in the prior arts shown in FIG. 1 and depicted in the Japanese Patent Application Laid-Open No. 10-138506, as the relief valve and the pressure regulator are connected between the (air) pressure pump and the ink tank (ink cartridge), they are actuated for controlling the compressed air delivered from the (air) pressure pump to the ink tank (ink cartridge). Accordingly, since its space for installing a large part such as the relief valve or the pressure regulator is essential, the ink jet printer will become large in the overall size and be increased in the production cost. Also, since the flow of the compressed air to be delivered to the ink cartridge is determined by the volume of the pressure regulator provided at the front side (the upstream side) of the ink cartridge, its pressure applied to the printing head will be varied depending on the remaining amount of the ink in the ink cartridge.
For controlling the compressed air with ease and less cost, a mechanism has been proposed where an orifice is provided in the air supply conduit extending from the air pump to the air chamber of the ink cartridge for discharging the compressed air generated by the air pump from the orifice to control the pressure and conduct the purging action (For example, see Japanese Patent Application Laid-Open No. 2004-58348, Paragraphs 0031 to 0035 and FIG. 6).